1. Field of the Invention
This invention relates to an ultrasonic diagnostic apparatus, more particularly to an improved ultrasonic diagnostic apparatus which enables noninvasive observation and examination of an afflicted portion of the circulatory system or of other tissue within the body.
2. Description of the Prior Art
The art of using ultrasonic waves in the diagnosis of diseases of the circulatory system has been practically applied in a wide range of fields. Ordinarily, ultrasonic examination of the circulatory system has fallen into two main categories: the method involving the imaging of various organs and the method involving the measurement of the flow velocity of blood and other body fluids. The former of these methods has been widely used to produce tomographic images of the heart, arteries and veins using A-mode imaging, B-mode imaging or a modification of one of these modes. In the latter method, ultrasonic waves are directed into the blood flow and the blood flow velocity is determined using the Doppler effect. This method is highly effective as a non-invasive means for early discovery of diseases of the circulatory system of the brain, for treatment of such diseases and for evaluation etc. of the effect of medicines on the circulatory system of the brain.
In the former method, however, there have been disadvantages in that the conventionally employed image display device permits observation of only the tomographic image, making it necessary to derive numerical values by measuring the displayed image and complicating the diagnostic procedure, and in that it has been difficult to electrically store the data derived by such measurement together with the image. As a result, this method has had ltitle practicability in actual diagnostic situations.
In particular, it has been extremely difficult to make accurate measurement in cases where the object under observation includes a moving member. Such a case arises, for example, in the examination of the heart and other organs of the circulatory system where the organ or the blood flowing through it are kept in constant motion by the pulsation of the heart.
Moreover, although the conventional methods mentioned above wherein an image is displayed through the use of an ultrasonic pulse beam or the blood flow velocity etc. are measured using the Doppler effect have been put to practical application in the examination of the circulatory system, these two methods have been employed independently of one another so that it has been impossible to carry out realtime observation of the relationship between the state of motion and the blood flow velocity in the actual portion of the organ where motion occurs. As a consequence, it has not always been possible to carry out an adeuate examination.
Another problem of the conventional methods concerns the importance of knowing the amount of arterial blood flow, particularly that in the brain circulatory system, in carrying out a proper diagnosis of diseases of the brain circulatory system. For obtaining the amount of blood flow with the conventional apparatuses, it has been necessary to separately obtain the blood vessel diameter from an A-mode image and the blood flow velocity by the Doppler effect and then to carry out a separate calculation by, for example, a computer. Te procedure is thus very complicated and is totally incapable of providing appropriate real-time diagnostic information. What is more, even the measurement of the diameter of the blood vessel cannot be carried out with precision.
In this connection it is known that when the flow velocity of blood etc. is to be measured using the Doppler effect of ultrasonic waves, it is important to properly select the angle of ultrasonic wave transmission and reception with respect to the direction of blood flow, and that optimum results are obtained when, as shown in FIG. 5, this angle is set at 60.degree..
In fact, however, it is generally impossible to determine the direction in which a blood vessel runs within a living body so that with the conventional apparatus the method used has been to attach a Doppler probe to the surface of the body so as to form an angle of approximately 60.degree. with respect to the presumed direction of the blood vessel being subjected to measurement. As a result, the conventional method of measuring blood flow velocity by the Doppler effect has had the shortcoming of including a large error factor.